On the lack of southern hemisphere polar mesosphere summer echoes

Abstract

We report VHF radar observations of the southern high‐latitude mesopause region using wind profilers that were installed recently on King George Island, Antarctica, and Ushuaia, Argentina. Briefly, our observations, which were made during January and February 1993, show almost no evidence of so‐called polar mesosphere summer echoes, or PMSE. Since these echoes are a predominant feature of the northern high‐latitude mesosphere in summer, their absence in the southern hemisphere is both surprising and intriguing. In this paper we present evidence demonstrating the virtual absence of the echoes and demonstrate that our systems were capable of detecting them had they been present. We also outline some of the consequences of this intriguing result, which are supported by observed hemispheric differences in polar mesospheric clouds, mesospheric temperatures, upper atmospheric gravity wave activity, and mean circulation patterns.

First observations of polar mesosphere summer echoes in Antarctica

“…We concluded that Antarctic P MSEs, if they existed at all, had to be at least 34 to 44 dB weaker than their Northern Hemispheric counterparts. We also reported, as the note added in proof in our previous study [Balsley et al, 1995], that a more thorough analysis of the first year's using refined noise reduction techniques yielded one very weak PMSE return that lasted for a few hours.…”

“…Until January 15, 1994, the radar system employed at the Machu Picchu site during both the 1992-1993 and the 1993-1994 campaigns was the same system reported by Balsley et al [1995]. This early system used a single system that was switched manually between three antennas fixed to point to the vertical and to 15 ø off vertical toward the north and east [Sarango et al, 1994].…”

Differences in near‐mesopause summer winds, temperatures, and water vapor at northern and southern latitudes as possible causal factors for inter‐hemispheric PMSE differences

“…One reason proposed for the weaker and more sporadic PMSE returns in the southern hemisphere is that the summer upper mesospheric temperatures in that hemisphere are somewhat warmer [Balsley et al, 1995;Hall, 1995;Woodman et al, 1999]. Verification of this idea is difficult, since, until recently, only a few studies of high-latitude summertime upper mesospheric temperatures in the two hemispheres have been published [Labitzke and Barnett, 1981;Barnett and Comey, 1985;Thomas, 1995].…”

Aspect sensitivity measurements of polar mesosphere summer echoes using coherent radar imaging

“…Since the initial report of PMSE, similar echoes have been detected at mid-latitudes (Reid et al, 1989;Thomas et al, 1992), and at Southern polar latitudes (Woodman et al, 1999). However, there is a disparity in the amount of PMSE activity observed at southern latitudes compared with northern latitudes (Balsley et al, 1995). During the ensuing years, a rich body of literature has developed in an attempt to explain PMSE, among which are several review papers (Röttger et al, 1988;Cho and Kelley, 1993;Cho and Röttger, 1997).…”